The luminosity determination for the ATLAS detector at the LHC during
collisions at Formula: see text 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several ...luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of Formula: see text is obtained for the Formula: see text of
collision data delivered to ATLAS at Formula: see text 8 TeV in 2012.
A search for singly produced vector-like
quarks, where
can be either a
quark with charge Formula: see text or a
quark with charge Formula: see text, is performed in proton-proton collisions recorded ...with the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 20.3 fbFormula: see text and was produced with a centre-of-mass energy of Formula: see text TeV. This analysis targets Formula: see text decays where the
boson decays leptonically. A veto on massive large-radius jets is used to reject the dominant Formula: see text background. The reconstructed
-candidate mass, ranging from 0.4 to 1.2 TeV, is used in the search to discriminate signal from background processes. No significant deviation from the Standard Model expectation is observed, and limits are set on the Formula: see text cross-section times branching ratio. The results are also interpreted as limits on the
coupling and the mixing with the Standard Model sector for a singlet
quark or a
quark from a doublet.
quarks with masses below 0.95 TeV are excluded at 95 % confidence level, assuming a unit coupling and a BRFormula: see text, whereas the expected limit is 1.10 TeV.
The large rate of multiple simultaneous proton-proton interactions, or pile-up, generated by the Large Hadron Collider in Run 1 required the development of many new techniques to mitigate the adverse ...effects of these conditions. This paper describes the methods employed in the ATLAS experiment to correct for the impact of pile-up on jet energy and jet shapes, and for the presence of spurious additional jets, with a primary focus on the large 20.3 Formula: see text data sample collected at a centre-of-mass energy of Formula: see text. The energy correction techniques that incorporate sophisticated estimates of the average pile-up energy density and tracking information are presented. Jet-to-vertex association techniques are discussed and projections of performance for the future are considered. Lastly, the extension of these techniques to mitigate the effect of pile-up on jet shapes using subtraction and grooming procedures is presented.
A search for neutral Higgs bosons of the minimal supersymmetric standard model (MSSM) and for a heavneutral Formula: see text boson is performed using a data sample corresponding to an integrated ...luminosity of 3.2 fbFormula: see text from proton-proton collisions at Formula: see text Formula: see text recorded by the ATLAS detector at the LHC. The heavy resonance is assumed to decay to a Formula: see text pair with at least one Formula: see text lepton decaying to final states with hadrons and a neutrino. The search is performed in the mass range of 0.2-1.2 Formula: see text for the MSSM neutral Higgs bosons and 0.5-2.5 Formula: see text for the heavy neutral Formula: see text boson. The data are in good agreement with the background predicted by the Standard Model. The results are interpreted in MSSM and Formula: see text benchmark scenarios. The most stringent constraints on the MSSM Formula: see text-Formula: see text space exclude at 95 % confidence level (CL) Formula: see text for Formula: see text Formula: see text in the Formula: see text MSSM scenario. For the Sequential Standard Model, a Formula: see text mass up to 1.90 Formula: see text is excluded at 95 % CL and masses up to 1.82-2.17 Formula: see text are excluded for a Formula: see text of the strong flavour model.
A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment ...in Formula: see text proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 Formula: see text of analyzed data. Results are interpreted within simplified models that assume
-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95 % confidence level on the mass of the gluino is set at 1.51 Formula: see text for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 Formula: see text are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector.
The results of a search for gluinos in final states with an isolated electron or muon, multiple jets and large missing transverse momentum using proton-proton collision data at a centre-of-mass ...energy of Formula: see text are presented. The dataset used was recorded in 2015 by the ATLAS experiment at the Large Hadron Collider and corresponds to an integrated luminosity of 3.2 fbFormula: see text. Six signal selections are defined that best exploit the signal characteristics. The data agree with the Standard Model background expectation in all six signal selections, and the largest deviation is a 2.1 standard deviation excess. The results are interpreted in a simplified model where pair-produced gluinos decay via the lightest chargino to the lightest neutralino. In this model, gluinos are excluded up to masses of approximately 1.6 Te V depending on the mass spectrum of the simplified model, thus surpassing the limits of previous searches.
The result of a search for pair production of the supersymmetric partner of the Standard Model bottom quark (Formula: see text) is reported. The search uses 3.2 fbFormula: see text of
collisions at ...Formula: see text TeV collected by the ATLAS experiment at the Large Hadron Collider in 2015. Bottom squarks are searched for in events containing large missing transverse momentum and exactly two jets identified as originating from
-quarks. No excess above the expected Standard Model background yield is observed. Exclusion limits at 95 % confidence level on the mass of the bottom squark are derived in phenomenological supersymmetric
-parity-conserving models in which the Formula: see text is the lightest squark and is assumed to decay exclusively via Formula: see text, where Formula: see text is the lightest neutralino. The limits significantly extend previous results; bottom squark masses up to 800 (840) GeV are excluded for the Formula: see text mass below 360 (100) GeV whilst differences in mass above 100 GeV between the Formula: see text and the Formula: see text are excluded up to a Formula: see text mass of 500 GeV.
A search is performed for a heavy particle decaying into different flavour dilepton pairs (Formula: see text, Formula: see text or Formula: see text), using 3.2 fbFormula: see text of proton-proton ...collision data at Formula: see text TeV collected in 2015 by the ATLAS detector at the Large Hadron Collider. No excess over the Standard Model prediction is observed. Limits at the 95 % credibility level are set on the mass of a Formula: see text boson with lepton-flavour-violating couplings at 3.0, 2.7 and 2.6 TeV, and on the mass of a supersymmetric Formula: see text sneutrino with
-parity-violating couplings at 2.3, 2.2 and 1.9 TeV, for Formula: see text, Formula: see text and Formula: see text final states, respectively. The results are also interpreted as limits on the threshold mass for quantum black hole production.
Measurements of normalized differential cross-sections of top-quark pair production are presented as a function of the top-quark, Formula: see text system and event-level kinematic observables in ...proton-proton collisions at a centre-of-mass energy of Formula: see text. The observables have been chosen to emphasize the Formula: see text production process and to be sensitive to effects of initial- and final-state radiation, to the different parton distribution functions, and to non-resonant processes and higher-order corrections. The dataset corresponds to an integrated luminosity of 20.3 fbFormula: see text, recorded in 2012 with the ATLAS detector at the CERN Large Hadron Collider. Events are selected in the lepton+jets channel, requiring exactly one charged lepton and at least four jets with at least two of the jets tagged as originating from a
-quark. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations. The results are in fair agreement with the predictions over a wide kinematic range. Nevertheless, most generators predict a harder top-quark transverse momentum distribution at high values than what is observed in the data. Predictions beyond NLO accuracy improve the agreement with data at high top-quark transverse momenta. Using the current settings and parton distribution functions, the rapidity distributions are not well modelled by any generator under consideration. However, the level of agreement is improved when more recent sets of parton distribution functions are used.
A search has been made for supersymmetry in a final state containing two photons and missing transverse momentum using the ATLAS detector at the Large Hadron Collider. The search makes use of ...Formula: see text of proton-proton collision data collected at a centre-of-mass energy of 13 TeV in 2015. Using a combination of data-driven and Monte-Carlo-based approaches, the Standard Model background is estimated to be Formula: see text events. No events are observed in the signal region; considering the expected background and its uncertainty, this observation implies a model-independent 95 % CL upper limit of 0.93 fb (3.0 events) on the visible cross section due to physics beyond the Standard Model. In the context of a generalized model of gauge-mediated supersymmetry breaking with a bino-like next-to-lightest supersymmetric particle, this leads to a lower limit of 1650 GeV on the mass of a degenerate octet of gluino states, independent of the mass of the lighter bino-like neutralino.
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